2.1 Brain Tumors
Brain tumors are among the leading cause of death among young children and adults. A survey by the American Cancer Society has documented that 13,300 people died of brain tumors in 1995 and predicated that over 17,900 would die in 1996 (Parker et al., 1996, CA Cancer J. Clin., 46:5-28). The number of deaths due to brain tumors has been increasing at a significant rate each year. On average, 25,000 Americans are diagnosed with brain cancer yearly. Brain tumors claim the lives of more children than any other form of cancer except leukemia.
The increased incidence of brain tumors is not only evident in children but also in adults. It has been documented that a significant increase in mortality has occurred in adult primary malignant tumors between 1982 and 1996 (Parker et al., 1996, CA Cancer J. Clin., 46:5-28). Glioblastomas, astrocytomas and meningiomas are the most common brain tumors that affect adults (Thapar and Laws, 1993, CA Cancer J. Clin., 43:253-271).
The transformation of normal human brain cells into gliomas occurs as a result of the accumulation of a series of cellular and genetic changes (Sehgal, 1998 Cancer Surv., 25:233-275; vonDiemiling et al., 1995 Glia 15:328-338; Furnari et al., 1995, J. Surg. Oncol. 67:234). These genetic alterations include the loss, gain or amplification of different chromosomes. These genetic changes lead to altered expression of proteins that play important roles in the regulation of normal cell proliferation. Several common genetic alternations at the chromosomal level (loss of 17p, 13q, 9p, 19, 10, 22q, 18q and amplification of 7 and 12q) have been observed (Sehgal et al., 1998, J. Surg. Oncol. 57:23; vonDiemiling et al., 1995, Glia 15:328-338; Furnari et al., 1995, Cancer Surv. 25:233-275). These alterations lead to changes in the expression of several genes (p53, RB, INFα/β, CDKN2, MMAC1, DCC, EGFR, PDGF, PDGFr, MDM2, GLI, CDK4 and SAS) during the genesis and progression of human gliomas (Sehgal, 1998, J. Surg. Oncol. 67:234; vonDiemiling et al., 1995, Glia 15:328-338). Recent studies have suggested that altered expression of several other genes (MET, MYC, TGFβ, CD44, VEGF, NCAML1, p21wafl/Cipl, trkA, MMRs, C4-2, D2-2) and proteins (cathepsins, tenascin, matrix metalloproteases, tissue inhibitors of metalloproteases, nitric oxide synthetase, integrins, IL 13 receptor, Connexin 43, uPAR's extracellular matrix proteins and heat shock proteins) are associated with the genesis of human gliomas (Sehgal, 1998, J. Surg. Oncol. 57:234). Taken together, these findings point to the fact that accumulation of multiple genetic mutations coupled with extensive changes in gene expression may be a prerequisite in the etiology of human gliomas. Despite identification of these genetic alterations, the exact series of events that leads to the genesis of human gliomas is not clear.
Glioblastoma multiforme are high grade astrocytomas that grow very rapidly and contain cells that are very malignant (Laws and Thapar, 1993, CA Cancer J. Clin., 43:263-271). The molecular basis of glioblastoma multiforme occurrence may involve systematic events at the chromosomal level or at a gene expression level. These may include inactivation of tumor suppressor genes, activation of oncogenes or specific translocations at the chromosomal level. Some genetic changes at the chromosomal level and gene expression level have been well documented for other brain tumors (Furnari et al., 1995, Cancer Surv., 25:233-275). For example, it has been documented that loss of tumor suppressor(s) genes at chromosome 10, mutations in p53, or overexpression of epidermal growth factor receptor, may be major events leading to glioblastoma multiforme. A number of other genes such as EGFR, CD44, β4 integrins, membrane-type metalloproteinase (MT-MMP), p21, p16, p15, myc, and VEGF have been shown to be overexpressed in different types of brain tumors (Faillot et al., Neurosurgery, 39:478-483; Eibl et al., 1995, J. of Neurooncol., 26:165-170; Previtali et al., 1996, Neuropathol. Exp. Neurol., 55:456-465; Yamamoto et al., 1996, Cancer Res., 56:384-392; Jung et al., 1995, Oncogene, 11:2021-2028; Tsuzuki et al., 1996, Cancer, 78:287-293; Chen et al., 1995, Nature Med., 1:638-643; Takano, et al., Cancer Res., 56:2185-2190; Bogler et al., 1995, Glia, 15:308-327). Other genes such as p53 show mutations in the majority of brain tumors (Bogler et al., supra). How the interplay of one more of these genes leads to tumorigenesis is not known but most likely multiple steps are required for neoplastic transformation. The exact series of events that lead to initiation or progression of glioblastoma are not known at present and useful markers for early detection of brain tumors are lacking.
2.2 CXCR-4
Chemokine receptors play an important role in the chemotaxis of T cells and phagocytic cells to areas of inflammation. CXCR-4 was first identified as a cDNA that was amplified using degenerate primers made against leukocyte chemotactic factor receptors (N-formyl peptides, C5a and IL-8) and was termed HM89 (Endres et al., 1996, Cell 87:745). Ligand binding analysis showed that HM89 was not a N-formyl peptide receptor, but sequence analysis clearly demonstrated that it is a member of the G protein coupled receptor family. Cytogenetic analysis indicates that HM89 is localized to human chromosome 2q21 (Beni et al., 1996, Nature 382:829). HM89 was later re-cloned using a rabbit IL-8 receptor cDNA upon screening a human monocyte library and was named LESTR (leukocyte derived seven transmembrane domain receptor (Nagasawa et al. 1996, Nature 382:635); and was again cloned and identified as a co-factor for HIV-1 fusion and entry into CD4+ cells (De Risi et al., 1996, Nature, Genetics 14:457). This co-factor was identical to the previously cloned HM89, and because of its role as a fusion protein between the HIV-1 virus and CD4+ cells it was designated as “fusin”. Fusin in conjunction with CD4 is sufficient to allow HIV-1 entry into non-permissive murine 3T3 cells (De Risi et al., 1996, Nature, Genetics 14:457). Sequence analysis indicated that HM89, LESTR and fusin are all the same gene and because of chemo-attraction properties, these genes are now termed CXC-chemokine receptor-4 (CXCR-4). Recently, it is shown that the CD4-independent infection by HIV-1 was mediated by the CXCR-4 receptor (Feng et al., 1996, Science 172:872). The ligand for CXCR-4 was recently cloned and termed PBSF/SDF-1 (Pre-B-cell growth stimulating factor/Stromal cell derived factor-1) (Engelhard et al., 1997, Neurosurgery 41:886). Transgenic mice that lack PBSF/SDF-1 died prenatally and their B-cells and myeloid progenitors were severely reduced in numbers (Harihabu et al., 1997 J. Biol. Chem. 272:28726). This result clearly demonstrates that PBSF/SDF-1 is responsible for B-cell lymphoesis and bone marrow myelopoiesis.
Recent studies demonstrate that CXCR-4 functions as a co-receptor with CD4 for the entry of T-cell tropic strains of HIV into target cells (Nomura et al., 1993, Int. Immunol. 5:1239; Federsppiel et al., 1993, Genomics 16:707). The mechanism by which HIV-1 interacts with the CXCR-4 chemokine receptor and CD4+ molecules during infection is unclear. It was also demonstrated that HIV-2 infection of CD4-cells can occur rapidly by utilizing the HIV-1 co-factor CXCR-4 receptor (Loctscher et al., 1994, J. Biol. Chem. 269:232). Interaction and cytopathic effects caused by entry of HIV-2 into CD4-cells were inhibited by a monoclonal antibody to the CXCR-4 protein (Doranz et al., 1997, Immunol. Resh. 16:15) (Feng et al., 1996, Science 272:872). The role of CXCR-4 in HIV infection was further strengthened when its introduction into human and nonhuman CD4-cells allowed HIV-2 infection (Doranz et al., 1997, Immunol. Res. 16:15) (Feng et al., 1996, Science 272:872).
Citation of references herein shall not be construed as an admission that such references are prior art to the present invention.